The present invention relates to a structure of a magnetic disk drive, and in particular to a magnetic head driving mechanism for an air bearing head slider.
The magnetic disk drive of this kind employs an air bearing head slider. The head slider closely follows a rotating disk surface at a constant spacing owing to the air flow caused by rotation of the disk in its recording or reproducing operation. On the other hand, the head slider contacts the disk surface while the disk is stopped. A suspension arm supports the head slider and is mounted on a carriage for moving the head slider in the radial direction of the magnetic disk. A stepping motor mechanically engages the carriage for positioning the head at a target track on the surface of the rotating disk. In the recording or reproducing operation, the head slider is rapidly accelerated and decelerated for radially accessing different data tracks and is stopped on the target track on the rotating disk surface.
In this head driving mecnanism, when the head stops on the target track, the head slider oscillates in the radial direction due to the inertial force of the head driving mechanism. Therefore, a considerable period is required to dampen the oscillation of the head. This oscillatory period is included in the access time of the disk drive. In other words, the disk drive cannot record or reproduce the data on the magnetic disk during the oscillatory period. Accordingly, the oscillation of the head should be damped as fast as possible in order to shorten the access time of the disk drive.
To this end, a conventional disk drive employs an electric damping of the stepping motor of the head driving mechanism. In the manner of the electric damping, a damping pulse is supplied to the stepping motor immediately after the stepping pulse has been supplied for rotating the stepping motor in the accessing direction and the head has been positioned on the target track. The damping pulse has a relatively low voltage and gives the rotary force in the reverse direction to the accessing direction.
The electric damping can reduce the oscillatory period of the head to some degree but is insufficient to obtain further reduction of the oscillatory period. Further, the control for supplying the damping pulse to the stepping motor is complicated.
On the other hand, the magnetic disk of the disk drive of this kind has a circular CSS (Contact Start Stop) zone on its surface for contacting the head slider when the disk stops. The CSS zone is disposed on the outer or inner circumferences of the R/W (Read/Write) zone where the data is recorded. The disk drive positions the head on the CSS zone after recording or reproducing operation has finished, and then, stops the disk rotation.
This positioning operation for the head to the CSS zone is indicated by the program for the computer system including the disk drive. Therefore, each job program requires the steps for carrying out the positioning operation for the head to the CSS zone after the final step. However, some programmers often compose a job program that lacks the positioning operation steps and have the program executed by the computer system. In this case, the disk drive stops the disk rotation with the head positioned on the R/W zone. Therefore, the head slider gradually falls and contacts the disk surface in the R/W zone in response to the decrease of the rotating speed of the disk, and finally, contacts the disk surface. In this state, if the head slider moves in the radial direction, the R/W zone of the disk surface is rubbed in the radial direction by the head slider and the R/W zone is damaged, i.e., "head crash" is occurred.
Similarly, the head slider rubs the R/W zone in the radial direction of the disk when the power supply to the disk drive is stopped by a power interruption while the disk drive is in a recording or reproducing operation.
Furthermore, when the disk drive is shipped, the head is positioned on the CSS zone. However, the head slider may move in the radial direction the disk and rub the R/W zone owing to considerable shock inflicted on the disk drive during the shipment. The "head crash" effect also occurs in this case.
The inventor of the present invention proposed a locking mechanism for a head driving mechanism disclosed in Japanese Utility Model Application No. 37002/1983. In this mechanism, a lever means engageable to the rotary axis of the stepping motor is provided for preventing the stepping motor from rotating while the disk drive is shipped. However, since the lever means is operated by hand and the operating portion of the lever means is disposed on the outer surface of the disk drive housing, this locking operation requires excess labor and cannot be carried out in the situation that the disk drive is assembled within the housing of a computer system.